[2] After he returned to Paris, there is no record of him, but about 1745 he was in Berlin, where he published eight etchings (1747–48) of plans and elevations for St Hedwig's Church (today's St. Hedwig's Cathedral), Berlin, which he produced in collaboration with Georg Wenzeslaus von Knobelsdorff, until recently the chief architect to Frederick II of Prussia; the church was eventually built to a modified version of the plan, by Johann Boumann, from June 1748, and Johann Gottfried Büring, in 1772–3.
For him he designed the formal water-garden at Schwerin, but built nothing; his project for Ludwigslust remained on paper, and his assistant, Johann Joachim Busch began the work in 1763, after Le Geay's departure.
He added a ballroom to the schloss at Rostock (Eriksen 1974; Erouart 1982) but after quarrelling with the King in 1763, Le Geay seems to have built little.
He spent two years, 1766–67, in England (Eriksen 1974:200), fruitlessly, though Sir William Chambers took the opportunity to copy some of his drawings,[3] then returned to Paris, where he published four extravagantly idiosyncratic suites of etchings of fountains, ruins, tombs, and vases, dated 1767-68, which were collected as Collection de Divers Sujets de Vases, Tombeaux, Ruines, et Fontaines Utiles aux Artistes Inventée et Gravée par J.-L.
They provide a large array of neoclassical motifs in the goût grec, but their presumed origin in Rome in the 1740s,[4] has been disproved (Erouart 1982), though they show the influence of Giambattista Piranesi.